Metal organic chemical vapor deposition (MOCVD) for producing III-V films on various substrates are well known and well documented in the literature. A few references to this subject, all disclosures of which are incorporated herein by reference, include U.S. Pat. Nos. 3,101,280, 3,218,203, 3,224,913, 3,226,270, 3,261,726, 3,312,570, 3,312,571, 3,342,551, 3,364,084, 4,368,098, and 4,404,265.
Chemical doping of materials, particularly semiconductor materials, is carried out in a similar manner to epitaxial growth of films by MOCVD. However, in doping, the substrate material is placed in the reaction chamber and lower levels of the metal-yielding compound are introduced.
Arsine (AsH.sub.3) had been the standard arsenic source for MOCVD processes for epitaxial growth films, such as III-V films. However, due to the hazard posed by this toxic and gaseous material, substitutes for arsine are sought for MOCVD processes as well as arsenic doping processes.
As an alternative to arsine, alkyl arsines have been used in MOCVD and doping processes. Initially, trialkyl arsines were tried. While these compounds are less hazardous than arsine, they have the disadvantage of tending to deposit carbon along with the metals. Accordingly, dialkyl arsines and monoalkyl arsines are finding favor for MOCVD and doping processes, as described, for example in U.S. Pat. Nos. 4,734,514 and 4,814,203, the teachings of which are incorporated herein by reference.
A further difficulty with known arsenic compounds when forming III-V films is that although the metal molar ratio of arsenic to the metal of group III metal compounds, e.g., Ga, is 1:1; a huge excess of arsenic compound relative to gallium compound must be passed through the reactor. When using arsine, it must be supplied at a molar ratio of about 100:1 relative to a gallium compound. When using an alkyl arsine, the molar ratio is still about 30:1. It would be desirable to reduce this ratio.
It is further desirable that the arsenic-containing compound introduced into the reaction chamber contain a high percentage of arsenic.